1. Field of the Invention
This invention relates to a system for estimating residual service time of a work vehicle, and more specifically to a system for estimating residual service time of a work vehicle such as a hydraulic excavator which digs out and removes earth, sand and broken rocks at a mine or the like.
2. Description of the Related Art
Work vehicles such as hydraulic excavators are employed to dig out earth, sand and the like and then to transport and remove them. As a great deal of load is applied to the work vehicles during such work, a variety of measures have been proposed concerning their maintenance and service [for example, Japanese Patent Application Laid-Open (Kokai) No. SHO 59-98935].
Different from general vehicles, work vehicles such as hydraulic excavators are often employed at sites remote from urban areas. If a work vehicle should run out of fuel for its engine, the work vehicle immediately stops. If this happens, it is no longer possible for the work vehicle to continue the work so that the efficiency of the work is considerably impaired.
On the other hand, a load which applies to a work vehicle substantially varies depending on the nature of work. This makes it difficult for an operator to estimate how much fuel would be consumed by the work vehicle. Therefore an operator often fails to refuel a work vehicle in time so that the work vehicle runs out of fuel and is no longer able to continue the work.
To avoid the above-mentioned running-out of fuel in work vehicles, many conventional work vehicles are equipped with a device which displays a warning sign or the like or generates a warning sound when the fuel level has decreased to such a level that the work vehicle can work only for an additional 1 hour under a maximum load. Based on the warning from the above-mentioned device, the operator requests refueling to a supervision center by a radio communication equipment or a mobile telephone. As another measure, a control system has been proposed which, as described in Japanese Patent Application Laid-Open (Kokai) No. HEI 4-265434, lowers an engine speed to a work-permitting minimum level to save the fuel consumption by a work vehicle when the fuel level has become low.
In a vast work site such as a strip (or open-pit) mine, many work vehicles are used from the viewpoint of improved productivity. Such a work site generally has several tank trucks available for refueling work vehicles. Each of these tank trucks visits its assigned work vehicles one after one to refuel them so that the work vehicles do not run out of fuel.
In the conventional device that produces warning when the fuel level has decreased to such a level as allowing a work vehicle to work only for additional 1 hour under a maximum load, the operator may ignore the warning and continue the work to achieve an improvement in productivity because he knows through experience that the fuel tank still contains fuel in an amount far more than that required for operating the work vehicle for 1 hour. In such a case, the work vehicle may not be refueled in time even if he requests refueling immediately after he becomes aware that the fuel level in the fuel tank has become low. As a result, the operator has no choice other than simply stopping the work until a tank trucks arrives. This problem has taken place frequently.
In the above-described conventional measure in which a tank truck visits and refuels work vehicles one after one, fuel is replenished to a fuel tank of each work vehicle to ensure avoidance of running-out of fuel even if a lot of fuel still remains in the fuel tank. More frequent refueling to the fuel tank is therefore needed than usual. As the work vehicle has to be stopped once upon each refueling, the more frequent refueling leads to an increase in work-suspending time. This has become a cause for an impaired efficiency of work. Especially at a site where a three-shift system is adopted, the serviceability ratio of work vehicles has reached 90% or still higher. In such a case, an increase in work-suspending time due to refueling leads directly to a reduction in the efficiency of work. To ensure avoidance of fuel running-out, it is essential to reserve tank trucks and their operators sufficiently. Extremely large expenses are therefore needed for such tank trucks and operators.